Metal vapor arc microwave switch

ABSTRACT

An improved microwave switch is disclosed wherein an arc is struck between metallic electrodes creating a metal vapor or plasma therebetween. This plasma, in one embodiment, is allowed to diffuse into the waveguide, thereby opening the switch and shortcircuiting the waveguide. A septum within the waveguide is used to deflect the plasma from the windows at either side of the switch, thereby preventing a metallic layer from building up on the windows which would induce reflection within the waveguide.

United States Patent [72] Inventor John M. Anderson Scotia, N.Y. [21] Appl. No. 23,256 [22] Filed Mar. 27,1970 [45] Patented Oct. 5, 1971 [73] Assignee General Electric Company [54] METAL VAPOR ARC MICROWAVE SWITCH 10 Claims, 6 Drawing Figs.

[52] U.S. Cl 315/39, 333/13, 313/178, 313/198 [51] 1nt.Cl 1-101j 7/46, HOlj 17/80 [50] Field of Search 315/39; 333/13; 313/178, 197, 198

[56] References Cited UNITED STATES PATENTS 2,697,800 12/1954 Roberts 315/39 2,819,422 11/1958 Gates 313/198 2,821,658 1/1958 Naugler 315/39 3,323,003 5/1967 Goldiem. 315/39 3,331,988 7/1967 Laffery... 313/178 X 3,439,223 4/1969 Wada 315/39 3,465,205 9/1969 Laffery 313/178 X Primary ExaminerHerman Karl Saalbaeh Assistant Examiner-Saxfield Chatmon, Jr.

Attorneys-John F. Ahern, Paul A. Frank, Julius J. J.

Zaskalicky, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman PATENTEU um 5mm 351 1.008

' sum 2 or 2 in ve n t or.- r/o/m M Anderson.

METAL VAPOR ARC MICROWAVE SWITCH This invention relates to microwave switches, and in particular to a microwave switch utilizing a plasma as the switching element.

In the past, microwave switches, known as TR switches, have been utilized to isolate a microwave transmitter from a receiver. Further, such devices have been utilized to control the flow of microwave energy.

Problems with previous types of switches include lack of precise timing of the switching action and a relatively narrow frequency range over which the switches can be utilized. Known microwave arc switches generally include arc electrodes and rely on the power of the transmitted microwave signal to initiate the arc. Others, with a trigger electrode, also rely on the transmitted microwave signal to supply the energy for the arc. Such systems, even with triggering, are subject to jitter, i.e., time variations in the switching action.

The known microwave arc switches also tend to be narrow band devices since the switch is frequently incorporated with quarter-wave stubs which are obviously only one-quarter wavelength long at a given frequency. In addition, metal vapor arc microwave switches tend to fog the window used to isolate the evacuated switch chamber from the remainder of the waveguide. The fogging is caused by the depositing of metal vapor from the arc electrodes onto the window.

In view of the foregoing, it is therefore an object of the present invention to provide a microwave switch in which the switching time is accurately controlled.

It is another object of the present invention to provide a microwave switch of substantially reduced jitter.

It is a further object of the present invention to provide a microwave switch which does not rely on the signal strength of a microwave signal for its operation.

Another object of the present invention is to provide a wide band microwave switch.

A further object of the present invention is to provide a microwave switch which does not relay on tuning stubs for proper operation.

Yet another object of the present invention is to prevent the fogging of the switch chamber windows.

The foregoing objects and other advantages are achieved by the present invention in which there is provided in one embodiment, a vacuum gap comprising a set of main electrodes and a centrally located trigger electrode, positioned adjacent an opening in the side of a section of waveguide. The section of waveguide is suitably sealed at each end and the vacuum gap suitably enclosed so that the region thus contained may be evacuated. Appropriate potentials are applied to the main electrodes and, upon a trigger pulse being applied to the trigger electrode, an electrical discharge is obtained between the main electrode. If, for example, copper is used for the main electrodes, a plasma with a relatively heavy electron density is formed in the copper vapor evaporated from the main electrodes. This plasma is then allowed to flow into the waveguide section via the opening and the switch opens, i.e., the plasma reflects microwave energy, thereby preventing its passage through the waveguide section. After the arc terminates, the plasma disappears very rapidly and the switch closes thereby allowing microwave radiation to pass through the waveguide section.

A more complete understanding of the present invention may be obtained from the following detailed description taken in conjunction with the attached drawings in which:

FIG. 1 illustrates one form of the present invention in which the arc gap is across the waveguide section.

FIG. 2 is a perspective view of another form of the present invention in which the are gap is across the waveguide section.

FIG. 3 is an end view of the embodiment illustrated in FIG. 2.

FIG. 4 illustrates another form of the present invention in which the arc gap is adjacent to the waveguide section.

FIG. 5 illustrates anotherembodiment of the present invention in which the arc gap is adjacent to the waveguide section.

FIG. 6 illustrates another form of the present invention in which the vacuum seal windows are protected.

Referring to FIG. 1 there is illustrated a section of waveguide 10 having first and second windows 11 and 12, respectively, at each end thereof. Windows 11 and 12 are transparent to microwave radiation and serve as a vacuum seal for waveguide section 10. Positioned along the length of waveguide section 10 are two quarter wavelength stubs l3 and 14 attached to opposite sides of the waveguide. Surrounding the quarter wavelength stubs l3 and 14 are vacuum envelopes 15 and 16, respectively, which serve to seal off the quarter wavelength stubs so that waveguide section 10 may be evacuated. Positioned within quarter wavelength stubs l3 and 14 are electrodes 18 and 19 which define an arc gap 24 which traverses waveguide section 10. Lines 17 and 20 serve to connect the respective electrodes to a suitable source of potential sufficient to cause an arc to be maintained across gap 24. A trigger electrode 21 is illustrated as being contained within the electrode 19. The electrode 19 has a hollowed out central portion for containing the trigger electrode which is spaced therefrom by an insulating member 22.

The microwave switch illustrated in FIG. I operates as follows: A trigger pulse is coupled to the trigger electrode 21 which induces a spark on the electrodes 21 and 19. This spark evaporates electrode material from the electrode 19 which then, upon passing into arc gap 24, lowers the dielectric constant of the spark gap thereby enabling an arc to traverse the gap and maintain itself so long as appropriate potentials are applied to lines 17 and 20. The electrical breakdown of the gap occurs in a very small fraction of a microsecond and a plasma with relatively high electron density forms in the vapor of electrode material evaporated from the electrons. The electrodes may, for example, comprise copper. Thus, as can be seen, the microwave switch can be made to turn on very rapidly. Further, the microwave switch as illustrated in FIG. 1 is not dependent upon the input power to the waveguide section 10 for the maintenance of the plasma. Upon termination of the maintenance potential applied to lines 17 and 20 the plasma rapidly dissipates, some of which returns to the electrodes and can be reevaporated upon the next induced are from the trigger electrode 21.

The electrode configuration of FIG. 1 is frequency dependent in that the quarter wavelength stubs assure a low voltage standing wave ratio (VSWR) only at a narrow range of frequencies in the off condition.

FIG. 2 illustrates a microwave switch which can be effectively used to allow operation over a wider range of frequencies. Since FIGS. 2 and 3 illustrate different views of the same embodiment of the present invention, they will be described together. In FIG. 2, waveguide section 10 has inserted therein a pair of ridge portions 30 and 31 which are tapered to the opposite walls of the waveguide section. Located within one of the ridged portions is an aperture 32 which enables a trigger electrode to be inserted into the waveguide section. Located between electrodes 30 and 31 is a central, perforated electrode 33. A trigger electrode 34 is inserted through aperture 32 into the ridged portion of element 30. Vacuum seals 35, 36, and 37 are provided at each of the electrodes so that the waveguide section 10 may be evacuated. In FIG. 3 there is indicated a second aperture portion 38 which may be provided as desired for a further trigger element.

The operation of the embodiment illustrated in FIGS. 2 and 3 is similar to that illustrated in FIG. 1. A trigger pulse initiates the generation of a plasma which then forms between electrodes 30, 31, and 33. So long as a sustaining voltage is applied to electrodes 30, 31, and 33, the plasma will be maintained and the high electron density thereof will serve to reflect the microwave energy within the waveguide section thereby performing the function equivalent to opening a switch. As with the embodiment shown in FIG. 1, the maintenance of the plasma is not dependent upon the power level of the microwave energy within the waveguide section, although it is appreciated that at very. high power levels the microwave energy may maintain the are. This, however, relates more to the problem of extinguishing the are than maintaining it.

FIG. 4 illustrates another embodiment of the present invention wherein the electrodes and trigger assembly are not located within the waveguide section but rather are located adjacent thereto. As shown in FIG. 4, waveguide section 10 contains windows 11 and 12 which serve as a vacuum seal. Surrounding electrodes l8, l8, and 19 is a vacuum envelope 15 which serves to seal the whole assembly. Electrodes 18, 18', and 19 may be generally cylindrical in shape and are symmetrically oriented about aperture 40 in the side of waveguide section 10. Contained within electrode 19 is trigger electrode 21 which is spaced therefrom by a suitable insulating member. Trigger electrode 21 is illustrated as containing a trigger gap 41 which serves to aid in the generation of the plasma. Trigger electrode 21 may comprise any suitable material, such as titanium hydride.

The operation of the apparatus as illustrated in FIG. 4 is as follows: A trigger pulse applied to trigger electrode 21 initiates a spark. If, for example, the trigger electrode assembly is composed of titanium hydride, the arc causes hydrogen or other stored active gas to be released from the titanium hydride. This gas is readily ionized within the gap and serves as one of the constituents of the plasma. If a low vapor pressure metal is utilized, the metal ions are boiled off and ionized to produce the ion electron plasma. The plasma thus formed flows out from electrodes 18 and 19 through aperture 40 in the side of waveguide section 10 and fills the region of the waveguide adjacent aperture 40. The plasma which diffuses into waveguide section 10 through aperture 40 blocks microwave radiation thus action as an open switch. Upon cessation of the maintenance voltage to main electrodes 18 and 19, the plasma formed is rapidly dissipated again, some of which returns to the electrode material.

In FIG. 5 there is illustrated another embodiment of the present invention wherein electrodes 51 and 52 are of a long configuration and are spaced adjacent to slit aperture 40. In this embodiment, trigger electrode 21 is placed adjacent to one of the main electrodes in a nonsymmetrical relationship.

The embodiment of FIG. 5 operates as described above, that is, a trigger source applies a pulse to trigger electrode 21 inducing a voltage across gap 41 in the trigger electrode surface. This causes a breakdown of the vacuum within waveguide section 10 and the heat of discharge causes gas stored in the trigger electrode to be released and ionized. This further reduces the dielectric strength of the gap between the main electrodes and an arc is induced between electrodes 51 and 52. Again, if a low vapor pressure metal is utilized, the metal ions are boiled off and ionized to produce the plasma. This plasma is then allowed to diffuse into waveguide section 10 thereby reflecting the microwave radiation. As with all the embodiments of the present invention, the maintenance of the plasma is not dependent upon the strength of the microwave radiation but rather is merely dependent upon appropriate voltages being applied to main electrodes 51 and 52.

In FIG. 6 there is illustrated a suitable modification for the microwave switches of the present invention in which the plasma and electrode material evaporated by the are are prevented from becoming deposited upon windows at either end of waveguide section 10. As shown in FIG. 6 the plasma or source of metal vapor 55 may cause the effusion of metal vapor throughout the waveguide during the opening of the switch element. This metal vapor, if allowed to become deposited upon windows 11 or 12, would soon induce reflections within the waveguide substantially reducing the VSWR of the waveguide section. In order to prevent this, a septum 56 is inserted in the waveguide between plasma 55 and windows 11 or 12. As illustrated in FIG. 6, plasma ions and neutral molecules traveling along either path 57 or 58 will be prevented from reaching window 11 by the interposition of septum 56. Septum 56 intercepts the metal ions, which are presumably moving in straight paths from a metal vapor arc, without introducing an appreciable impedance to the microwave propagation in the waveguide section 10. The lengths of the folded portions of septum 56 as well as its overall length may be adjusted for minimum microwave reflection and loss. The use of septum 56 presupposes that waveguide section 10 is straight; if waveguide section 10 is curved, then the waveguide itself may be used to intercept the metal ions as they travel toward the windows.

Although a specific embodiment of the present invention has been described, it will be apparent to those skilled in the art that numerous modifications may be made within the spirit and scope of the present invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A microwave switch comprising:

a evacuated section of waveguide having opposed quarter wave stubs extending from the sides thereof at a given point along the length of the section,

massive cylindrical electrode means positioned in each of said stubs, one of said electrode means having a hollow central portion,

said cylindrical electrode means forming electrically isolated anode and cathode of an arc gap,

trigger means located within said hollow central portion for initiating an arc across said gap, and hence across the waveguide section from one side to the other, and

means for supplying appropriate voltages to said trigger anode and cathode, whereby, upon initiation of an arc, a plasma containing electrode material is formed and extends across said waveguide section to block the flow of microwave energy through the waveguide section.

2. A microwave switch as set forth in claim 1 further comprising:

radio frequency transparent window means at each end of said waveguide section for sealing said waveguide section, and

septum means positioned in said waveguide section between said plasma and said window means for preventing the depositing of electrode material on said window means.

3. A microwave switch comprising:

a. an evacuated hermetically sealed waveguide section having a microwave permeable window at either end thereof;

b. at least one lateral aperture in the wall of said section and an hermetically sealed appendage adjacent each said aperture;

0. means juxtaposed adjacent said aperture for producing upon the application of an electrical signal thereto an electron-ion plasma of sufficient density to provide a short circuit for microwave energy in said waveguide adjacent said aperture and comprising, c a pair of massive discharge electrodes adapted to carry an electric arc discharge in a cold cathode mode of operation and defining therebetween an arcing gap,

c each of said primary discharge electrodes being electrically insulating from said waveguide section and from each other,

0 trigger electrode means juxtaposed adjacent said areing gap and adapted to strike a spark discharge with one of said primary discharge electrodes upon the application of an electrical pulse thereto to establish conducting species within said arcing gap and establish an electric discharge therebetween.

4. A microwave switch as set forth in claim 3, wherein said plasma producing means comprises means for generating an electric discharge within said waveguide section.

5. A microwave switch as set forth in claim 4, wherein said waveguide section has a pair of quarter wavelength stubs positioned on opposite sides of said waveguide and including said aperture, and said plasma producing means comprises:

first and second electrode means positioned one each in said stubs, and

trigger electrode means positioned relative to one of said electrode means for initiating the generation of an electric discharge whereby a portion of the electrode material from said electrode means will evaporate, thereby forming a plasma containing said electrode material and having a relatively high electron density for preventing the transmission of microwave energy through said waveguide.

6. A microwave switch as set forth in claim 4, wherein said plasma producing means comprises:

first and second ridge portions on opposite sides of and within said waveguide section at least one of said portions containing an aperture positioned coincident with an aperture in said waveguide section, said ridge portions forming a first electrode,

central electrode means positioned between said ridge portions, thereby forming a second electrode, and

trigger electrode means positioned within said aperture for initiating an electric discharge between said first and second electrodes whereby a plasma is formed for preventing the transmission of microwave energy through said waveguide.

7. A microwave switch as set forth in claim 3, wherein said plasma producing means comprises means for generating an electric discharge adjacent to said waveguide and for coupling said plasma thus produced to the interior of said waveguide section by way of said aperture.

8. A microwave switch as set forth in claim 7, wherein said means for generating an electric discharge comprises symmetrically oriented first, second, and trigger electrode means positioned adjacent to said waveguide section wherein said trigger electrode, upon being suitably activated, initiates an electric discharge between said first and second electrodes causing electrode material to evaporate, forming a relatively high electron density plasma which diffuses into said waveguide section through said aperture.

9. A microwave switch as set forth in claim 8 further comprising:

vacuum seal means at each end of said waveguide section and surrounding said electrode whereby the chamber thus formed may be evacuated, and

a source of potential coupled to said electrodes whereby said electric discharge occurs independently of the power level of the microwave signal within said waveguide section.

10. A microwave switch as set forth in claim 8, wherein said first, second, and trigger electrodes are asymmetrically oriented and wherein said aperture is an elongated slit in said waveguide section. 

1. A microwave switch comprising: a evacuated section of waveguide having opposed quarter wave stubs extending from the sides thereof at a given point along the length of the section, massive cylindrical electrode means positioned in each of said stubs, one of said electrode means having a hollow central portion, said cylindrical electrode means forming electrically isolated anode and cathode of an arc gap, trigger means located within said hollow central portion for initiating an arc across said gap, and hence across the waveguide section from one side to the other, and means for supplying appropriate voltages to said trigger anode and cathode, whereby, upon initiation of an arc, a plasma containing electrode material is formed and extends across said waveguide section to block the flow of microwave energy through the waveguide section.
 2. A microwave switch as set forth in claim 1 further comprising: radio frequency transparent window means at each end of said waveguide section for sealing said waveguide section, and septum means positioned in said waveguide section between said plasma and said window means for preventing the depositing of electrode material on said window means.
 3. A microwave switch comprising: a. an evacuated hermetically sealed waveguide section having a microwave permeable window at either end thereof; b. at least one lateral aperture in the wall of said section and an hermetically sealed appendage adjacent each said aperture; c. means juxtaposed adjacent said aperture for producing upon the application of an electrical signal thereto an electron-ion plasma of sufficient density to provide a short circuit for microwave energy in said waveguide adjacent said aperture and comprising, c1 ) a pair of massive discharge electrodes adapted to carry an electric arc discharge in a cold cathode mode of operation and defining therebetween an arcing gap, c1 ) each of said primary discharge electrodes being electrically insulating from said waveguide section and from each other, c2) trigger electrode means juxtaposed adjacent said arcing gap and adapted to strike a spark discharge with one of said primary discharge electrodes upon the application of an electrical pulse thereto to establish conducting species within said arcing gap and establish an electric discharge therebetween.
 4. A microwave switch as set forth in claim 3, wherein said plasma producing means comprises means for generating an electric discharge within said waveguide section.
 5. A microwave switch as set forth in claim 4, wherein said waveguide section has a pair of quarter wavelength stubs positioned on opposite sides of said waveguide and including said aperture, and said plasma producing means comprises: first and second electrode means positioned one each in said stubs, and trigger electrode means positioned relative to one of said electrode means for initiating the generation of an electric discharge whereby a portion of the electrode material from said electrode means will evaporate, thereby forming a plasma containing said electrode material and having a relatively high electron density for preventing the transmission of microwave energy through said waveguide.
 6. A microwave switch as set forth in claim 4, wherein said plasma producing means comprises: first and second ridge portions on opposite sides of and within said waveguide section at least one of said portions containing an aperture positioned coincident with an aperture in said waveguide section, said ridge portions forming a first electrode, central electrode means positioned between said ridge portions, thereby forming a second electrode, and trigger electrode means positioned within said aperture for initiating an electric discharge between said first and second electrodes whereby a plasma is formed for preventing the transmission of microwave energy through said waveguide.
 7. A microwave switch as set forth in claim 3, wherein said plasma producing means comprises means for generating an electric discharge adjacent to said waveguide and for coupling said plasma thus produced to the interior of said waveguide section by way of said aperture.
 8. A microwave switch as set forth in claim 7, wherein said means for generating an electric discharge comprises symmetrically oriented first, second, and trigger electrode means positioned adjacent to said waveguide section wherein said trigger electrode, upon being suitably activated, initiates an electric discharge between said first and second electrodes causing electrode material to evaporate, forming a relatively high electron density plasma which diffuses into said waveguide section through said aperture.
 9. A microwave switch as set forth in claim 8 further comprising: vacuum seal means at each end of said waveguide section and surrounding said electrode whereby the chamber thus formed may be evacuated, and a source of potential coupled to said electrodes whereby said electric discharge occurs independently of the power level of the microwave signal within said waveguide section.
 10. A microwave switch as set forth in claim 8, wherein said first, second, and trigger electrodes aRe asymmetrically oriented and wherein said aperture is an elongated slit in said waveguide section. 